1. Field of the Invention
The present invention relates to information processing apparatuses, information processing terminals, information processing methods, information processing systems, recording media, and programs, and more particularly, to an information processing apparatus, an information processing terminal, an information processing method, an information processing system, a recording medium, and a program suited to a case in which data is transmitted and received through a network.
2. Description of the Related Art
There has been conventionally a technology in which a server for storing compressed audio data and a player (reproduction) apparatus for reproducing compressed audio data are connected through a network, and the user operates the player apparatus to receive compressed audio data from the server, to decode the received compressed audio data, to convert the audio data to non-compressed data, and to apply digital-to-analog (D/A) conversion to the non-compressed data to reproduce the desired music data.
When data is distributed through a wide area network, such as the Internet, by a protocol which cannot specify a transfer path on the network, for example, since the transfer rate is determined by a portion having the lowest communication rate in the data transfer path, that is, a bottleneck, if such a bottleneck exists in the transfer path, it takes a very long time to transmit and receive a large amount of data. To solve this problem, there are many data compression techniques for compressing data while reducing transfer errors. Such audio-data compression techniques include MPEG-1 audio layer-3 (MP3), advanced transform acoustic coding (ATRAC), and WAV. Even when the amount (data transfer rate) of data to be distributed and received per unit period is small, if audio data is compressed and transmitted and received, comfortable data transfer is performed.
Not only when compressed audio data is distributed through a wide area network, such as the Internet, but when, for example, a network is configured in a house, and a server which has recorded compressed audio data and a terminal which can receive compressed audio data, decode it, and reproduce the original data are used, the user can play back the music and enjoy it at any place within the network environment by using a compact player apparatus which has not recorded audio data in its inside recording unit or to which a recording medium that has recorded audio data is not mounted.
A conventional system will be described below by referring to FIG. 1, in which a server and an audio player terminal which can reproduce audio data are provided in a network, the server records compressed audio data, and the audio player terminal decodes compressed audio data to reproduce the original data.
A server 1 and an audio player terminal 2 are connected to a network through a hub 3. The server 1 and the audio player terminal 2 may be connected to the hub 3 by wires or by radio. The hub 3 is connected to another network 5, such as the Internet, through a router 4. In FIG. 1, only one audio player terminal 2 is shown, and a description thereof is made. A plurality of audio player terminals may be connected to the hub 3.
A control section 11 of the server 1 is formed of a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM), and controls the processing of the server 1. A communication section 12 transmits and receives data to and from the audio player terminal 2, connected to the same network through the hub 3, and further, to and from other information processing apparatuses connected to the network 5 through the router 4, under the control of the control section 11. A compressed-audio-data recording section 13 records compressed audio data encoded in a predetermined format, such MP3, ATRAC, or WAV.
A control section 21 of the audio player terminal 2 is formed of a CPU, a ROM, and a RAM, and controls the processing of the audio player terminal 2. A display section 22 is formed, for example, of a liquid-crystal display (LCD), and displays text or an image according to the control of the control section 21. An operation input section 23 is formed, for example, of a button, a keyboard, a mouse, or a touch sensitive panel, receives an operation input of the user, and outputs it to the control section 21.
A communication section 24 transmits and receives information to and from the server 1 through the hub 3 according to the control of the control section 21. A decoder 25 receives compressed audio data from the server 1 through the communication section 24, and decodes (decompresses) it to convert the compressed audio data having a predetermined format to linear pulse-code-modulation (PCM) data.
Linear PCM data is obtained by sampling analog audio data at a constant interval, by quantizing it, and then, by converting it to binary data, and is equal to digital audio data obtained by applying A/D conversion to the analog audio data. The quality of reproduced sound depends on the sampling frequency and the number of quantization bits.
A buffer 26 receives the linear PCM data obtained by decoding from the decoder 25, buffers it, and outputs it to a D/A conversion section 27 at predetermined timing. The D/A conversion section 27 converts the input linear PCM data to an analog signal, and outputs it to a speaker 28 to reproduce the sound.
Processes performed by the server 1 and the audio player terminal 2 will be described next. It is assumed that the compressed-audio-data recording section 13 has recorded various kinds of musical-piece data as compressed audio data having a predetermined format, together with the titles thereof.
The control section 21 of the audio player terminal 2 generates a request for asking the server 1 to send a list of musical pieces (titles thereof) of the compressed audio data recorded in the compressed-audio-data recording section 13 of the server 1, and sends the request to the server 1 through the communication section 24 and the hub 3.
Generally, text information, such as the list of musical pieces transferred between the server 1 and the audio player terminal 2, is transmitted and received by using a Hypertext Transfer Protocol (HTTP) in many cases. In HTTP, a request for sending information is sent from a client (the audio player terminal 2 in FIG. 1) to a server (the server 1 in FIG. 1), and the server sends back a response to the request. In other words, one batch of communication is formed of one set of a request and a response, and is called a session.
The control section 11 of the server 1 receives a request from the audio player terminal 2 through the communication section 12, and transmits the list of the musical pieces of the compressed audio data recorded in the compressed-audio-data recording section 13 as a response to the request, to the audio player terminal 2 through the communication section 12 and the hub 3.
The control section 21 of the audio player terminal 2 receives the input of the list of the musical pieces through the communication section 24, and displays it on the display section 22 or records it in an internal RAM such that the list is displayed on the display section 22 when the user inputs a predetermined operation at the operation input section 23.
The user refers to the list of the musical pieces displayed on the display section 22 to select a desired musical piece and to instruct to play back the musical piece by using the operation input section 23. The control section 21 receives a signal indicating the user's operation inputs from the operation input section 23, generates a request for sending the compressed audio data corresponding to the desired musical piece of the user, and sends it to the server 1 through the communication section 24 and the hub 3.
The control section 11 of the server 1 receives the request from the audio player terminal 2 through the communication section 12, searches the compressed audio data recorded in the compressed-audio-data recording section 13 for the compressed audio data corresponding to the user's desired musical piece, and outputs it as a response to the request to the audio player terminal 2 through the communication section 12 and the hub 3. When the transmitted compressed audio data is stereo audio data, for example, the transfer rate of the compressed audio data is about 64 Kbps to 320 Kbps.
The control section 21 of the audio player terminal 2 makes the decoder 25 decode the compressed audio data input through the communication section 24, buffers the decoded data in the buffer 26, converts the data into analog audio data in the D/A conversion section 27, and outputs it through the speaker 28 to play back the musical piece.
There are a method called stream transfer or stream distribution and a method called download distribution to transmit audio data from the server 1 to the audio player terminal 2. In stream distribution, the audio player terminal 2 can reproduce in real time audio data transmitted by the server 1. In the system shown in FIG. 1, while the audio player terminal 2 receives compressed audio data from the server 1, the audio player terminal 2 decodes the data and reproduce it in real time. In download distribution, the server 1 sends all data to the audio player terminal 2, and the audio player terminal 2 can perform a reproduction process when the audio player terminal 2 has received all the data. In the system shown in FIG. 1, after the audio player terminal 2 receives all compressed audio data, the audio player terminal 2 decodes the data to playback the original musical piece.
However, in stream distribution, the audio player terminal 2 needs to include a buffer memory having a capacity required for continuously decoding received compressed audio data and for playing back the original musical piece. In download distribution, the audio player terminal 2 needs to include a memory having a capacity required for temporarily storing all compressed audio data before decoding, or to have a structure to which an external recording medium for temporarily storing all compressed audio data can be mounted.
Since, as a unit for controlling processing executed by the audio player terminal 2, a central processing unit (CPU), a digital signal processor (DSP), or others having a processing capability of decoding compressed audio data received from the server 1 needs to be selected, the cost of the audio player terminal 2 is increased.
When the audio player terminal 2 can be carried by the user, for example, a battery is used as a power source of the audio player terminal 2. In such a case, since it is necessary to supply electric power required to make the CPU or the DSP perform decoding, the driving time of the battery is short or the battery becomes large.